The present invention relates to articles having a finely uneven surface (small dents and small projections) and, particularly, to micro optical elements and information recording medium substrates as well as a production process and composition for the same.
Optical parts such as CD-ROMS, other information recording media, plate microlenses (an array of a large number of microlenses arranged in parallel on a plate), Fresnel lenses and diffraction grating elements must have fine irregularities (small dents and small projections) on the surface. The fine irregularities on the surface function as a pit or tracking guide in an information recording medium or as a microlens or diffraction grating to focus or diffuse light in an optical part.
To form irregularities on the surface, there is known a process which comprises spreading an ultraviolet curable resin over a substrate uniformly and exposing the resin to ultraviolet radiation with the resin pressed with a mold having irregularities (JP-A 63-49702).
JP-A 62-102445 discloses a process for producing an article having irregularities on the surface by means of a so-called xe2x80x9csol-gel processxe2x80x9d which comprises coating a solution containing silicon alkoxide on a glass substrate and heating the substrate with the substrate pressed with a mold having irregularities to form irregularities. JP-A 6-242303 discloses a process for forming a plurality of layers on a substrate when a film having a thickness of several micrometers or more is formed by means of the sol-gel process. In this case, a solution or sol containing the constituents of each layer is poured over a completely solidified layer, which is formed by coating the solution or sol on the existing layer and heating the layer with the layer pressed with a mold, to form an upper layer.
However, the above prior art technologies have the following problems. Firstly, the ultraviolet curable resin has such low heat resistance that it decomposes or yellows at temperatures of 250xc2x0 C. or above. Therefore, a substrate having irregularities which is made of an ultraviolet curable resin cannot be subjected to a heat treatment such as soldering and is difficult to be mounted on a device.
In contrast to this, irregularities made of silicon alkoxide by the sol-gel process has high heat resistance and can be soldered. However, the sol-gel process has such a problem that a thick film cannot be formed. In fact, when a silicon alkoxide layer of several tens of micrometers is formed by the sol-gel process, fine cracks emerge on the surface of the layer. This is because large stress is produced on the surface due to a difference in the progress of a polycondensation reaction between the surface and the interior of this layer when a silicon alkoxide solution is gelled and solidified. Further, this stress sometimes causes the layer to peel off from the substrate.
An organopolysiloxane layer having irregularities and a thickness of several tens of micrometers can be formed by molding a plurality of organopolysiloxane layers sequentially. However, the production process is long, thereby boosting costs. In addition, since a solution for the next layer is poured after an under layer is completely cured, undesirable air easily enters in a space between the mold and the solution or sol, thereby reducing the dimensional accuracy of the irregularities.
The present invention has been made in view of the above problems of the prior art. It is an object of the present invention to provide a process for producing an article which has a finely uneven surface and high dimensional accuracy and whose surface film has high heat resistance, does not crack even if it is a single-layer film having a thickness of several tens to several thousands of micrometers and does not peel off from a substrate.
It is another object of the present invention to provide a composition for forming the above film.
It is still another object of the present invention to provide an article having an uneven surface which is produced by the process of the present invention.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by a process for producing an article having an uneven surface, comprising forming a film of a sol material between the substrate of the article and a mold in such a manner that the film is in close contact with these and heating the film to form a gelled film, which has a surface configuration that is the inversion of the surface configuration of the mold, on the surface of the substrate of the article, wherein the sol material contains (A) a silane compound represented by the following formula (1):
R2SiX2xe2x80x83xe2x80x83(1)
xe2x80x83wherein R is an alkyl group and X is an alkoxyl group or a halogen atom, and
(B) a silane compound represented by the following formula (2):
xe2x80x83Rxe2x80x2SiXxe2x80x23xe2x80x83xe2x80x83(2)
xe2x80x83wherein Rxe2x80x2 is a substituted or unsubstituted aryl group and Xxe2x80x2 is an alkoxyl group or a halogen atom.
According to the present invention, secondly, the above objects and advantages of the present invention are attained by an article having an uneven surface which is produced by the process of the present invention, wherein an organopolysiloxane film having irregularities is formed to a thickness of 1 xcexcm to 1 mm on the surface of the substrate of the article and contains 5 to 25 wt % of an alkyl group and 5 to 40 wt % of an aryl group.
According to the present invention, finally, the above objects and advantages of the present invention are attained by a composition for forming a film for producing an article having an uneven surface, which contains:
(A) a dialkyldialkoxysilane in an amount of 1 mol,
(B) a trialkoxysilane having an aryl group or substituted aryl group in an amount of 0.2 to 4 mol,
(C) an alcohol in an amount 0.3 to 3 times the total number of moles of the components (A) and (B),
(D) an acid catalyst in an amount 3 to 20 times the total number of moles of the components (A) and (B), and
(E) water in an amount 2 to 20 times the total number of moles of the components (A) and (B).